As a conventional flange structure, there is known a structure disclosed in the patent document 1. According to this conventional flange structure, in an exhaust manifold having multiple exhaust pipe connecting holes and a mounting hole for mounting it onto the cylinder head of an engine respectively formed in a board body, the board body is formed to have a swelling part projecting toward the exhaust flow-out side and including a vertical flange in the outer periphery thereof and an inclined end face, and the exhaust pipe connecting holes are formed in the inclined end face, whereby an exhaust pipe can be mounted on the vertical flange of this flange with an inclined angle.